B. Description of Proposed Boundary Modification

Modification to shift <600 acres of water and land from the Tracy Subbasin to the Solano Subbasin

Type of basin boundary revision

Jurisdiction Internal

Provide a narrative overview of the boundary modification request and how
the resulting modification would affect likelihood of sustainable management.

The boundary modification will affect stream boundary segment 16-17 of the Solano Subbasin and stream segment 6-7 of the Tracy Subbasin, which are based on the flowline from the National Hydrography Dataset for the San Joaquin River. The southern boundary of Sacramento County is similar to the flowline, except in the vicinity of West Island, where the County boundary is south of the island and the basin boundary is north of the island. The boundary modification will affect a 3-mile long portion of the 21-mile long common boundary between Sacramento County and Contra Costa County, and shift the current basin boundary up to 0.5 miles south to the Sacramento County boundary. The approximate 600-acre (440 acres of water and 140 acres of uninhabitable land) modification area will shift from the Tracy Subbasin to the Solano Subbasin, as part of the Sacramento County Groundwater Sustainability Agency (GSA).
The boundary modification will facilitate Sacramento County management of groundwater resources by shifting a very small unmanaged GSA area within the Tracy Subbasin to a much larger unmanaged GSA area in the Solano Subbasin, both areas were included in the Sacramento County GSA. The modification will not affect sustainable management because the nominal 600-acre area is located in the San Joaquin River. The area is comprised mostly of water (>70%) with the remainder known as West Island (<30%), which is uninhabited and undeveloped, except for two support structures for overhead power lines.

Attachment(s):

List of the existing basin(s)/subbasin(s) to be modified by this request

5-021.66 SACRAMENTO VALLEY - SOLANO

5-022.15 SAN JOAQUIN VALLEY - TRACY

Provide the proposed name for the new basin(s) or subbasin(s)

C. Initial Notification and Combination of Requests

Was an initial notification submitted to the Department?

Yes

List of submitted initial notification for the selected basin(s)/subbasin(s).

A map of adequate scale (no greater than 1:24,000; e.g., 1:10,000 is not acceptable) showing the proposed modified basin boundary in relation to the existing Bulletin-118 basin boundary and the local agencies that are within or bordering the existing and proposed basin.

Any information, if necessary, to enable DWR to satisfy the requirements of a responsible agency pursuant to the California Environmental Quality Act.

This BBM should not be subject to CEQA because of the de minimis impact on groundwater management in either the Tracy or Solano Subbasins. The modification area is less than 600 acres, comprised of less than 30% land (West Island) and over 70% water (San Joaquin River). The BBM will increase the area of the Solano Subbasin by 0.14% and decrease the area of the Tracy Subbasin by 0.17%.

E. General Information

Describe the lateral boundaries of the alluvial aquifer or aquifers that form the groundwater basin and the definable bottom of the basin. The description must be in terms that are clear, definite, and sufficiently detailed to allow an authoritative map of the proposed basin boundaries to be plotted using the given description.

The lateral boundaries of the Solano Subbasin are defined by 19 segments, including five County segments, five Water Agency segments, five Steam segments, two Watershed segments, one Transportation segment, and one Unknown segment that is quite short and traverses the Sacramento River from a Water Agency to the County line. The primary segment types are Stream and Watershed and the secondary types are County and Water Agency (DWR BBDescribe, 2018). The bottom of the basin can be defined by the base of fresh groundwater (Berkstresser, 1973), which varies from less than 400 feet below sea level along the southwestern corner of the subbasin, in the vicinity of the modification area, to over 3,200 feet below sea level in a small crescent area approximately 12 miles south/southeast of Davis.
West Island is uninhabited and groundwater conditions are not defined, as the 140-acre island is in the San Joaquin River.

F. Notice and Consultation

List all local agencies and public water systems affected by the basin(s) modification request.

Sacramento County GSA - Slightly greater area for GSA in Solano Subbasin
Solano Subbasin Groundwater Sustainability Agency-Slightly greater area for Solano Subbasin
Contra Costa County GSA - Slightly less area in Tracy Subbasin

Explain the methods used to identify interested local agencies and public water systems in the affected basin(s):

Provide information regarding the nature of consultations with affected or interested agencies. Attach and cite any copies of correspondences with local agencies and public water systems and/or any other persons or entities consulted.

See attached support letters from Solano Subbasin GSA, Contra Costa County GSA, Discovery Bay Community Services District GSA, East Contra Costa Irrigation District, and City of Antioch.
See attached emails to Solano Subbasin GSA and Contra Costa County GSA.

Attach a copy of all comments regarding the proposed boundary modification received by the requesting agency and a summary of any responses made by the requesting agency.

None through May 25, 2018

G. General Existing Groundwater Management

All requests for jurisdictional modification pursuant to Section 342.4 MUST include responses to the following questions.

Explain how sustainable groundwater management exists or could likely be achieved in the basin:

The 600-acre modification area will not affect groundwater management in the Solano Subbasin because the area is only 0.14% of the entire subbasin, is located in the middle of the San Joaquin River, does not utilize any groundwater, and will not likely utilize groundwater in the future. Sustainable groundwater management will likely be achieved in the Solano Subbasin through the coordinated efforts of the seven GSAs in their preparation of a single Groundwater Sustainability Plan. Sacramento County, as the GSA for the modification area and other nearby Delta areas, will coordinate with the other GSAs of the Solano Subbasin to produce a complete GSP, as documented in the January 2018 Memorandum of Understanding (attached).

Explain how the proposed boundary modification would affect the ability of adjacent groundwater basins to sustainably manage groundwater in those groundwater basins.

The Tracy Subbasin will not be affected by the boundary modification because groundwater is not and will not likely be developed on the small island (140 acres) within the ~600-acre modification area in the San Joaquin River.

Provide a historical summary of the sustainable management of groundwater levels in the proposed basin(s) or subbasin(s).

Groundwater levels are not available for West Island, as the island is uninhabited and in the San Joaquin River. The groundwater would be shallow, fluctuate with river levels, and have comparable water quality to the river.
The closest two wells are located south of the modification area in the Tracy Subbasin, including the 106-foot-deep Wilbur Deep Well (0.6 mile) and the 88-foot deep Blossom Well (1.1 miles). Both wells are part of the CASGEM program. At the Wilbur Deep Well, depths to groundwater (DtW) varied from 11 to 17 feet below ground (bg) between November 2014 and May 2015. At the Blossom Well, DtW varied from 32 to 35 feet bg between October 2014 and October 2017.
In the Solano Subbasin, the closest two wells include a CASGEM well (COSAC3) at Brannon Island State Recreation Area, 6.9 miles to the northeast, along the Sacramento River, and a Voluntary Well to the north 9.9 miles in the Montezuma Hills. At the 416-foot deep COSAC3 well, DtW varied from 32 to 38 feet bg between April 2015 and October 2107. At the 130-foot deep Voluntary Well (04N/02E-22P1), DtW varied from 50 to 62 feet bg between October 2014 and October 2017. Water levels are available for this well, beginning in 1992, and the fall data show three overall trends. During first 10 years of data (1992 ? 2003), the mean DtW was 45 feet bg and showed a variable, but small overall water level decline of 1.3 feet per year. Between November 2003 and October 2004, the water level decreased nearly seven feet and remained variably at that level (mean: 52 feet bg) during the next eight years (2004 - 2012) with a negligible downward trend. Between December 2012 and December 2013, the water level decreased nearly 13 feet, but recovered somewhat during the next two years and the mean DtW has been approximately 60 feet bg during the last three fall measurements (2015 - 2017).
Water level data are available for numerous wells further north in the Solano Subbasin but will not be affected by the basin boundary modification.

Discuss potential impacts to state programs resulting from the proposed boundary modification, including, but not limited to, the California Statewide Groundwater Elevation Monitoring (CASGEM), Groundwater Management Plans developed pursuant to AB 3030, Groundwater Sustainability Plans developed pursuant to the Sustainable Groundwater Management Act, any applicable state or regional board plans, and other water management and land use programs.

The basin boundary modification will not impact any state management program, including CASGEM.

H. Local Support

All requests for boundary modification must include the following:

Provide any evidence that sufficient information was provided to affected agencies and systems regarding the proposed boundary modification.

Please see attachments to Notice and Consultation F(3)(4).

Provide a list of all affected agencies and affected systems that submitted comments and/or documents in support or opposition to the proposed boundary. The agency submitting their support or opposition for a boundary modification must provide a copy of a resolution formally adopted by the decision-making body of the affected agency or system or a letter signed by an executive officer or other official with appropriate delegated authority who represents the agency or system. Attach copies of the resolution and/or signed letter detailing the support or opposition submitted.

Significant geologic and hydrologic features and conditions of the principle aquifer units, as appropriate, including information regarding the confined or unconfined nature of the aquifer, facies changes, truncation of units, the presence of faults or folds that impede groundwater flow, or other groundwater flow restricting features.

The department may waive this requirement for an internal boundary modification if the requesting agency is able to demonstrate that the proposed boundary modification is unlikely to affect sustainable groundwater management.

Sacramento County requests a waiver from this item because the 600-acre modification area is located within the San Joaquin River, is mostly covered by water (>70%), and likely will not use groundwater for any purpose in the future. Groundwater conditions beneath West Island will be highly dependent on the flow and quality of the river. The HCM topics will be addressed in the GSP for the Solano Subbasin and Sacramento County GSA will participate in the preparation of that GSP. Sustainable groundwater management will not be affected by this small modification.

L. Technical Studies for All Jurisdictional Modifications

Requests for a jurisdictional boundary must attach or provide a URL or upload a file for the following:

A water management plan that covers or is in the immediate vicinity of the proposed basin or portion of the proposed basin and satisfies the requirement of Water Code sections 10753.7(a) or 10727 by attaching one of the following:

An adopted groundwater management plan, a basin wide management plan, or other integrated regional water management program or plan.

Management pursuant to an adjudication action.

One or more technical studies that cover the relevant portion of a basin or subbasin and adjacent areas.

A statement of the existing and planned coordination of sustainable groundwater management activities and responsibilities where required.

Sacramento County is the GSA for much of the southwestern Delta area in the Solano Subbasin and the 600-acre modification area will be incorporated into a larger Sacramento County GSA in the Solano Subbasin. Sacramento County will continue to work with the other GSAs in Solano Subbasin to prepare and submit a GSP by January 2022 and to attain sustainable groundwater management in the Solano Subbasin by 2042.

Created on 05/17/2018 at 3:42PM,
last modified on 06/20/2018 at 7:44AM
and page generated on 09/15/2019 at 3:01AM